Crystal controlled oscillator



3ept, 7, 1937. TURNER 2,092,098

CRYSTAL CONTROLLED OS CILLATOR Filed Aug. 51, 1935 Patented Sept. 7, 1937 UNITED STATES PATENT OFFICE CRYSTAL CONTROLLED OSCILLATOR Alfred H. Turner, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application August 31, 1935, Serial No. 38,694

8 Claims. (Cl. 250-36 My invention relates to thermionic oscillators. The center grid electrode G2 is given a positive Specifically my invention relates to a piezocharge. Most of the electrons emitted at the electrical or crystal controlled oscillator having a cathode K will pass to the positive grid G2 but, negative resistance characteristic. since this electrode has a grid-like structure,

One of the objects of my invention is to consome of the electrons will pass through its meshes 5 trol the oscillatory frequency of a negative reand start toward the outermost plate or anode sistance oscillator. P which has a less high positive charge than the Another object is to control the frequency of center grid G2. The outer grid G3 with its negaa negative resistance oscillator by means of a tive charge, will repel some of the electrons 0 piezo-electric element. which will be turned and attracted to the more Afurther object lies in a piezo-electrically conpositive grid electrode G2. As the outer grid trolled negative resistance oscillator in which the G3 is made less negative, it will repel less elecpiezo-electric element is not subjected to eXcestrons to the center grid G2, and permit more to sive heating currents, and in which the output pass to the outer plate P. The positive potential circuit is substantially independent of the input of the outer plate P must not be made so high 15 circuit. that the outer control grid G3 will have little Additional objects will appear in the accomeffect on the electronic currents flowing to the panying specification and claims. outer plate. The outer control grid G3 must Figure I is a schematic diagram of a three turn back a substantial quantity of electrons electrode thermionic tube, to efficiently use the negative resistance charac- 20 Fig. II is a schematic diagram of a negative teristic just described.

resistance oscillator, and Thus we have a circuit in which increased Fig. III isa circuit diagram of one embodiment positive or less negative charges on a control of my invention. grid, cause decreased plate current. Decreased In Fig. I, a three electrode thermionic tube is current flowing through the resistor R will in- 25 illustrated. If the grid potential is made less crease the positive potential on center grid G2. negative, the plate current increases. Increased The instantaneous increased positive potentials, plate current through the plate resistance R deif fed to the control grid G3, will be in phase creases the plate potential. If the decreased to sustain oscillations. A capacity C of suitable plate potential were fed back to the grid, it would value between the center grid G2 and outer con- 30 be out of phase with the grid potential and the trol grid G3 is all that is required to feed back device would not show any positive feedback or properly phased potentials. oscillatory characteristics. If the phase in the If the inductance of the leads is negligible, plate circuit could be reversed, the output or the frequency of oscillation or time period deplate circuit energy would be fed back to the pends upon the product of the coupling capacity grid in proper phase to maintain oscillations. and resistance (T CR). The frequency may Expressed in other terms: if the plate current be made very low by using a large capacity and could be'made to decrease when the grid voltage a small resistance. The lowest frequency is is made more positive, the effects, or phases lim by the owest voltage drop across the would not be opposed but in proper relation to resistance which will sustain oscillations. The 40 sustain oscillations if the output currents were highest frequency is limited by the interelecfed back to the input. trode capacity of the thermionic tube and the Fig. II represents a circuit having the charelectron transit time. This upper limit of the acteristic of the arrangement suggested in the fundamental frequency is of the order of 20 description immediately above. Consider the megacycles. 45 central grid G2 a positive electrode, the outer The circuit shown in Fig. II will oscillate as a grid G3 as a control grid, and K as the cathode. so-called relaxation oscillator. Briefly a re- The effect of the first or inner grid G1 may be laXation oscillator is an electronic device having neglected for the moment. Electrons will leave a cycle of operation dependent upon the time the cathode K as represented by the dotted lines. required to charge and discharge a reactance. 50

is preferably by-passed by a capacity H.

' through a variable resistor 21.

Such oscillators are generally characterized by large oscillatory currents, anode currents approaching saturation, and oscillations oi an irregular frequency characteristic. I propose to overcome these defects and control the frequency of oscillation by making use of the first or inner grid G1. I shall also couple an output circuit to the outer plate circuit of Fig. II so that the operation of the circuit will not be materially affected.

In Fig. III, in a thermionic tube I, such as an RCA type 57, the heater 3 is connected to a source of energy 5. The cathode 1 is grounded through a self biasing resistor 9. The resistor Between the inner control grid l3 and the cathode is connected a piezo-electric crystal l5. A re-' sistor i? is shunted from control grid to cathode. A central grid electrode I9 is connected to a resistor 2! which is in turn connected to the positive terminal of the anode battery 23. The negative terminal of the anode battery is grounded. An outer grid electrode 25, which is located nearest the anode, is connected to ground A variable capacitor 29 is connected between the central and outer grid electrodes. The anode 3% is connected through a resistor 33 to a positive potential point 35 intermediate the ends of the anode bat- 7 characterized by a square wave form, and an tery. A coupling capacitor 31 is connected between the anode 33 and one output terminal 39. The other output terminal 4i may be grounded. A work circuit may be connected to the output terminals.

If the piezo-electric crystal is omitted from the circuit, the device will operate as a relaxation oscillator. The oscillations will have a frequency which is dependent upon the time constants of the elements. The oscillations will be abundance of harmonic frequencies. If the relative values of the variable capacitor 29 and the Variable resistor 2! are altered, the frequency of the relaxation oscillations will be varied. Such oscillations are not of constant frequency.

After the piezo-electric element is connected, the'relative values of the variable capacitor and variable resistor are altered until their time constant (T CR) is near the natural mode of vi- ='bration of the piezo-electric crystal, or a multiple or sub-multiple of said natural mode. At this period or frequency of vibration the relaxation oscillator will energize the crystal. Thereafter the crystal will oscillate at its own natural frequency and synchronize the relaxation oscillations. The energy to maintain the oscillations of the crystal is derived from the oscillator and is'fed across the inherent capacity between the inner and central grids. This capacity may be supplemented by a capacitor. The harmonic oscillations which are thus generated may be multiples or sub-multiples of the crystal frequency.

As is well known, certain crystals may have two natural modes of vibration. Each mode, or the frequencies of two modes may combine, and generate currents of a definite frequency. By adjusting the time constant of the relaxation oscillator to approximately any one of the natural modes or periods of oscillation of the crystal, the crystal will control the relaxation oscillations at the particular selected frequency or multiple or sub-multiple thereof. The crystal will then limit therelaxation oscillator to the particular fundamental frequency, its harmonics, or sub-har monics.

By way of example, the following table of constants and values may be helpful:

Thermz'om'c tubeRCA tube 57 Inner control grid to cathode resistance ohms 500,000 Self bias resistancedo 2,000 Central grid to posi anode battery do n 100,000 Outer grid to ground do 10,00010,000,000 Anode resistance do 1 0,000 Bypass capacity mfds 1.0 Variable coupling capacity do 0-50 Output coupling capacity do 1.0 Anode battery" 250 Anode voltage +25 Central grid shown. However, the illustration of one pre-' ferred embodiment of my invention, must not be taken as evidence that I intend to limit my invention except as required by the prior art and the appended claims.

I claim as my invention:

1. In an oscillator, a thermionic tube having a cathode, anode, and plurality of grid electrodes including an inner grid, a center grid, and an outer grid, a source of anode current including a negative terminal, a connection between said cathode and the negative terminal of said source,

a piezo-electric element efiectively connected between cathodeand said inner grid electrode, a resistance connected between the positive terminal of said anode current source and the center grid electrode, a resistance connected between the negative terminal of said anode current source and the outer grid electrode, a connection between said anode and a point having a potential less positive than the positive terminal of said anode source, a capacity coupling the centergrid and the outer grid, means for adjusting one of said resistances and said capacity to thereby establish oscillatory currents, and means for impressing said currents on said piezo-electric element to thereby cause said element to ural frequency.

2. In an oscillator, a thermionic tube'having a cathode, anode, and plurality of grid 'electrodes including an inner grid, a center grid, and

an outergrid, a source of anode current including a negative terminal, means for biasing said cathode positively with respect to one of said grid electrodes, a connection between said cathode and the negative terminal of said source, a piezo-electric element effectively connected between cathode and said inner grid electrode,a resistance con- 'nected between the positive terminal of said anvibrate at its nata cathode, anode, and plurality of grid electrodes including inner, center, and outer grids, a source of anode current including a negative f terminal, a piezo-electric element effectively connected between cathode and said inner grid electrode, a resistance connected between the positive terminal of said anode current source and the center grid electrode, a resistance connected between the negative terminal of said anode current source and the outer grid electrode, a connection between said anode and a point having a potential less positive than the positive terminal of said anode source, a variable capacity coupling the center grid and the outer grid, a biasing resistor connected between said cathode and the negative terminal of said source, means for adjusting one of said resistances and said capacity to thereby establish oscillatory currents, and means for impressing said currents on said piezoelectric element to thereby cause said element to vibrate at its natural frequency.

4. In an oscillator, a thermionic tube having a cathode, anode, and inner, outer and center grid electrodes, a source of anode current including negative and positive terminals, means for biasing said cathode positively with respect to one of said grid electrodes, a piezo-electric element effectively connected between cathode and said inner grid electrode, a resistance connected between the positive terminal of said anode current source and the center grid electrode, a resistance connected between the negative terminal of said anode current source and the outer grid electrode, a connection between said anode and a point having a potential less positive than the positive terminal of said anode source, a variable capacity coupling the center grid and the outer grid, a connection from said cathode to the negative terminal of said source, means for adjusting one of said resistances and said capacity to thereby establish oscillatory currents, and means for impressing said currents on said pieZo-electric element to thereby cause said element to vibrate at its natural frequency.

5. In a device of the character described a thermionic tube having cathode, inner grid, center grid, outer grid, and anode electrodes, a source of anode current, means for grounding the negative terminal of said source, a piezo-electric element effectively connected between cathode and said inner grid, a resistance connected between cathode and said inner grid, a resistance connected between the positive terminal of said anode current source and said center grid, a resistance connected between ground and said outer grid, a connection between said anode and a positive potential point intermediate the positive and negative terminals of said anode current source, a capacity connected between the center grid and the outer grid, means connecting said cathode and the negative terminal of said source, means for adjusting one of said resistances and said capacity to thereby establish oscillatory currents, and means for impressing said currents on said piezo-electric element to thereby cause said element to vibrate at its natural frequency.

6. In a device of the character of claim 5 means for biasing one of said grid electrodes negatively with respect to cathode.

'7. In a device of the character of claim 5 means for coupling said anode circuit with a pair of output terminals.

8. In an oscillator of the character described a thermionic tube having cathode, anode and inner, outer and centrally located grid electrodes, a source of current including positive and negative terminals, means for grounding said negative terminal, a resistance connecting the centrally located grid to said positive terminal, a resistance connecting the outer grid electrode to said negative terminal, a connection from said anode to a point of positive potential interme diate the aforementioned positive and negative terminals, a capacity coupling said central and outer grids whereby a negative resistance characteristic is established, a piezo-electric element connected between said inner grid and said cathode to synchronize the frequency of oscillations generated by said device, biasing means connecting said cathode and the negative terminal of said source, means for adjusting one of said resistances and said capacity to thereby establish oscillatory currents, and means for impressing said currents on said pieZo-electric element to thereby cause said element to vibrate at its natural frequency.

ALFRED H. TURNER. 

